enzymes

• Haemoglobin contains a prosthetic haem group which contains iron, permanently bound to the molecule to bind to oxygen.
• Enzymes are globular proteins, often referred to as biological catalysts as they speed up the rate of reaction of biological reactions in the body, such as digestion.
• Enzymes are easily affected by changes in temperature and pH.
• Enzymes are much more specific than chemical catalysts, and do not produce unwanted by-products and very rarely make mistakes.
• Cells can regulate the production and activity of enzymes based on their needs.
• The instructions to make enzymes are encoded in genes - if the gene has a mutation which alters the base sequence of the enzyme, the protein’s tertiary structure might be affected.
• The enzyme has an active site that has a specific shape that is only complementary to a certain type(s) of substrate.
• The active site is a cleft/indentation in the enzyme that is only 6-10 amino acids large.
• Enzymes may be part of a metabolic pathway, where each of reactants and intermediates act as substrates or metabolites for specific enzymes and form specific products for the next step.
• In an anabolic pathway, the smaller metabolites are used to synthesise larger molecules, using energy.
• In a catabolic pathway, metabolites are broken down into smaller molecules, releasing energy.
• Catalase is a eukaryotic enzyme present in peroxisomes that catalyses the breakdown of hydrogen peroxide, a potentially harmful chemical, a byproduct of many metabolic reactions, into water and oxygen.
• Catalase is used by white blood cells to kill invading pathogens.
• Enzymes are secreted from cells, so that they can act on the substrates in an external environment.
• Trypsin is made in the pancreas and works in the lumen of the small intestine, digesting proteins into peptides by hydrolysing peptide bonds.
• Amylase is made in the salivary glands and pancreas, and works in the mouth and small intestine, digesting starch into maltose (polysaccharide→disaccharide).
• Enzymes and substrates both have kinetic energy, so constantly move randomly.
• If the enzyme and substrate collide successfully, they form an enzyme-substrate complex.
• The substrate is either built up or broken down into the product(s), forming an enzyme-product complex while the product remains in the active site.
• The product is then released, but the enzyme is not used up in the reaction.
• Enzymes lower the activation energy because they bring the reactants close enough together to react, so that they do not need excessive heat to react.
• There are two hypotheses (no evidence proving either theory) which state how the enzyme and substrate fit together: Lock and key and Induced fit.
• Nucleoside reverse transcriptase inhibitors are used to treat HIV-positive patients as they inhibit enzymes used when making DNA from viral RNA template.
• ACE inhibitors inhibit Angiotensin converting enzyme (ACE) which is usually involved in metabolic reactions which increase blood pressure.
• Multi-enzyme complexes increase the efficiency of metabolic reactions without increasing substrate concentration, as they keep the enzymes and the substrates in the same vicinity, reducing diffusion time.
• ATPase is inhibited by cardiac glycosides in heart-muscle cells, allowing more calcium to enter into these cells, increasing muscle contraction, strengthening heartbeat.
• Coenzymes are organic cofactors which do not bind permanently and facilitate the binding of substrates to enzymes, many of which are vitamin derived.
• Prosthetic groups are small, non-protein molecules that are permanently attached to the enzyme.
• The greater the concentration of the non-competitive inhibitor, the greater the reduction in rate of reaction, as more enzymes’ active sites are disrupted.
• Many toxins exert their effects as they inhibit or inactivate enzymes, for example, KCN inhibits aerobic respiration and catalase by binding to an enzyme found in mitochondria, and snake venom inhibits acetylcholinesterase (AChE) by binding to the active site.
• Control of metabolic sequences involves cells not accumulating too much of a certain product, which may attach to the allosteric site of the first enzyme in the sequence, preventing the first enzyme from catalysing the first reaction, preventing the pathway from starting.
• Protease inhibitors are used to treat viral infections as they inhibit protease enzymes, ensuring that the viral coats cannot be made, so viruses cannot be replicated.
• A cofactor is a non-protein compound required for the enzyme’s activity to occur, and there are three types of cofactors: coenzymes, activators and prosthetic groups.
• End product inhibition is an example of negative feedback, as once the catalysed reaction has completed, the products may stay tightly bound to the active site, preventing any substrates from binding to the active site.
• Increasing the concentration of substrate has no effect on non-competitive inhibition.
• Activators are inorganic metal ions which temporarily bind to the enzyme and alter its active site, making the reaction more feasible.
• Non-competitive inhibitors bind to the allosteric site of the enzyme, changing the shape of the active site and preventing the binding of the substrate.
• The enzyme has an active site that is complementary to the shape of the substrate in the Lock and key hypothesis.
• The active site is still complementary to the shape of the substrate, but the substrate binding to the active site induces a change in the shape of the side chains of the enzyme, giving it a more precise conformation, allowing more efficient binding in the Induced fit hypothesis.
• The substrate forms non-covalent bonds to the active site.